2023 Vol. 42, No. 10

2023, 42(10): .
2023, 42(10): .
Articles$Physical Oceanography, Marine Meteorology and Marine Physics
The combined effects of North Atlantic Oscillation and Western Pacific teleconnection on winter temperature in Eastern Asia during 1980−2021
Ziqun Zhang, Hongyan Cui, Baoxu Chen, Hong Cai, Pin Li
2023, 42(10): 1-9. doi: 10.1007/s13131-023-2187-6
As important atmospheric circulation patterns in Northern Hemisphere (NH), the North Atlantic Oscillation (NAO) and the Western Pacific teleconnection (WP) affect the winter climate in Eurasia. In order to explore the combined effects of NAO and WP on East Asian (EA) temperature, the NAO and WP indices are divided into four phases from 1980−2021: the positive NAO and WP phase (NAO+/WP+), the negative NAO and WP phase (NAO−/WP−), the positive NAO and negative WP phase (NAO+/WP−), the negative NAO and positive WP phase (NAO−/WP+). In the phase of NAO+/WP+, the low geopotential height (GH) stays in north of EA at 50°−80°N; the surface air temperature anomaly (SATA) is 0.8−1℃ lower than Southern Asian. In the phase of NAO−/WP−, the center of high temperature and GH locate in the northeast of EA; the cold air spreads to Southern Asia, causing the SATA decreases 1−1.5℃. In the phase of NAO+/WP−, the high GH belt is formed at 55°−80°N. Meanwhile, the center of high SATA locates in the north of Asia that increases 0.8−1.1℃. The cold airflow causes temperature dropping 0.5−1℃ in the south of EA. The SATA improves 0.5−1.5℃ in south of EA in the phase of NAO−/WP+. The belt of high GH is formed at 25°−50°N, and blocks the cold air which from Siberia. The NAO and WP generate two warped plate pressure structures in NH, and affect the temperature by different pressure configurations. NAO and WP form different GH, and GH acts to block and push airflow by affecting the air pressure, then causes the temperature to be different from the north and south of EA. Finally, the multiple linear regression result shows that NAO and WP are weakened by each other such as the phase of NAO+/WP+ and NAO−/WP−.
Characteristics of extratropical cyclone variability in the Northern Hemisphere and their response to rapid changes in Arctic sea ice
Di Chen, Qizhen Sun
2023, 42(10): 10-22. doi: 10.1007/s13131-023-2277-4
Extratropical cyclones are critical weather systems that affect large-scale weather and climate changes at mid-high latitudes. However, prior research shows that there are still great difficulties in predicting extratropical cyclones for occurrence, frequency, and position. In this study, mean sea level pressure (MSLP) data from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) are used to calculate the variance statistics of the MSLP to reveal extratropical cyclone activity (ECA). Based on the analysis of the change characteristics of ECA in the Northern Hemisphere, the intrinsic link between ECA in the Northern Hemisphere and Arctic sea ice is explored. The results show that the maximum ECA mainly occurs in winter over the mid-high latitudes in the Northern Hemisphere. The maximum ECA changes in the North Pacific and the North Atlantic, which are the largest variations in the Northern Hemisphere, are independent of each other, and their mechanisms may be different. Furthermore, MSLP is a significant physical variable that affects ECA. The North Atlantic Oscillation (NAO) and North Pacific Index (NPI) are significant indices that impact ECA in the North Atlantic and North Pacific, respectively. The innovation of this paper is to explore the relationship between the activity of extratropical cyclones in the Northern Hemisphere and the abnormal changes in Arctic sea ice for the first time. The mechanism is that the abnormal changes in summer-autumn and winter Arctic sea ice lead to the phase transition of the NPI and NAO, respectively, and then cause the occurrence of ECA in the North Pacific and North Atlantic, respectively. Arctic sea ice plays a crucial role in the ECA in the Northern Hemisphere by influencing the polar vortex and westerly jets. This is the first exploration of ECAs in the Northern Hemisphere using Arctic sea ice, which can provide some references for the in-depth study and prediction of ECAs in the Northern Hemisphere.
Cross-shelf variation of internal tides west of the Dongsha Plateau in the northern South China Sea
Wei Yang, Ruixiang Li, Yanqing Feng, Huijie Xue
2023, 42(10): 23-35. doi: 10.1007/s13131-023-2251-1
We examine the cross-shelf variation of internal tides (ITs) west of the Dongsha Plateau in the northern South China Sea based on observations from 4 moorings deployed between August 2017 and September 2018. On the slope, the amplitude of diurnal baroclinic current ellipses are 5 times larger than that of barotropic currents. The baroclinic energy quickly dissipates during cross-shelf propagation, and barotropic currents become dominant on the shelf outside of the Zhujiang River Estuary, with the amplitude of semidiurnal barotropic current ellipses being 10 times larger than that of the baroclinic ones. Dynamic modal decomposition indicates the first baroclinic mode is dominant for both diurnal and semidiurnal ITs. The total horizontal kinetic energy (HKE) of the first three baroclinic modes shows spatiotemporal differences among the 4 moorings. On the slope, the HKE for diurnal ITs is stronger in summer and winter, but weaker in spring and autumn; for semidiurnal ITs there is a similar seasonal variation, but the HKE in winter is even stronger than that in summer. On the shallow shelf, both diurnal and semidiurnal ITs maintain a certain intensity in summer but almost disappear in winter. Further analysis shows that only the upper water column is affected by seasonal variation of stratification on the slope, variation of diurnal ITs is thus controlled by the semi-annual cycle of barotropic energy input from the Luzon Strait, while the incoherent baroclinic currents make a major contribution to the temporal variation of semidiurnal ITs. For the shelf region, the water column is well mixed in winter, and the baroclinic energy largely dissipates when ITs propagate to the shelf zone despite of a strong barotropic energy input from the Luzon Strait .
Wave hindcast under tropical cyclone conditions in the South China Sea: sensitivity to wind fields
Liqun Jia, Shimei Wu, Bo Han, Shuqun Cai, Renhao Wu
2023, 42(10): 36-53. doi: 10.1007/s13131-023-2227-1
Reliable wave information is critical for marine engineering. Numerical wave models are useful tools to obtain wave information with continuous spatiotemporal distributions. However, the accuracy of model results highly depends on the quality of wind forcing. In this study, we utilize observations from five buoys deployed in the northern South China Sea from August to September 2017. Notably, these buoys successfully recorded wind field and wave information during the passage of five tropical cyclones of different intensities without sustaining any damage. Based on these unique observations, we evaluated the quality of four widely used wind products, namely CFSv2, ERA5, CCMP, and ERAI. Our analysis showed that in the northern South China Sea, ERA5 performed best compared to buoy observations, especially in terms of maximum wind speed values at 10 m height (U10), extreme U10 occurrence time, and overall statistical indicators. CFSv2 tended to overestimate non-extreme U10 values. CCMP showed favorable statistical performance at only three of the five buoys, but underestimated extreme U10 values at all buoys. ERAI had the worst performance under both normal and tropical cyclone conditions. In terms of wave hindcast accuracy, ERA5 outperformed the other reanalysis products, with CFSv2 and CCMP following closely. ERAI showed poor performance especially in the upper significant wave heights. Furthermore, we found that the wave hindcasts did not improve with increasing spatiotemporal resolution, with spatial resolution up to 0.5°. These findings would help in improving wave hindcasts under extreme conditions.
Significant wave height forecasts integrating ensemble empirical mode decomposition with sequence-to-sequence model
Lina Wang, Yu Cao, Xilin Deng, Huitao Liu, Changming Dong
2023, 42(10): 54-66. doi: 10.1007/s13131-023-2246-y
As wave height is an important parameter in marine climate measurement, its accurate prediction is crucial in ocean engineering. It also plays an important role in marine disaster early warning and ship design, etc. However, challenges in the large demand for computing resources and the improvement of accuracy are currently encountered. To resolve the above mentioned problems, sequence-to-sequence deep learning model (Seq-to-Seq) is applied to intelligently explore the internal law between the continuous wave height data output by the model, so as to realize fast and accurate predictions on wave height data. Simultaneously, ensemble empirical mode decomposition (EEMD) is adopted to reduce the non-stationarity of wave height data and solve the problem of modal aliasing caused by empirical mode decomposition (EMD), and then improves the prediction accuracy. A significant wave height forecast method integrating EEMD with the Seq-to-Seq model (EEMD-Seq-to-Seq) is proposed in this paper, and the prediction models under different time spans are established. Compared with the long short-term memory model, the novel method demonstrates increased continuity for long-term prediction and reduces prediction errors. The experiments of wave height prediction on four buoys show that the EEMD-Seq-to-Seq algorithm effectively improves the prediction accuracy in short-term (3-h, 6-h, 12-h and 24-h forecast horizon) and long-term (48-h and 72-h forecast horizon) predictions.
Strip segmentation of oceanic internal waves in SAR images based on TransUNet
Kaituo Qi, Hongsheng Zhang, Jiaojiao Lu, Yinggang Zheng, Zhouhao Zhang
2023, 42(10): 67-74. doi: 10.1007/s13131-023-2206-6
The development of oceanic remote sensing artificial intelligence has made possible to obtain valuable information from amounts of massive data. Oceanic internal waves play a crucial role in oceanic activity. To obtain oceanic internal wave stripes from synthetic aperture radar (SAR) images, a stripe segmentation algorithm is proposed based on the TransUNet framework, which is a combination of U-Net and Transformer, which is also optimized. Through adjusting the number of Transformer layer, multi-layer perceptron (MLP) channel, and Dropout parameters, the influence of over-fitting on accuracy is significantly weakened, which is more conducive to segmenting lightweight oceanic internal waves. The results show that the optimized algorithm can accurately segment oceanic internal wave stripes. Moreover, the optimized algorithm can be trained on a microcomputer, thus reducing the research threshold. The proposed algorithm can also change the complexity of the model to adapt it to different date scales. Therefore, TransUNet has immense potential for segmenting oceanic internal waves.
Forty-year investigation of wave power in energetic region of Persian Gulf in Iranian territorial waters by using short-term and new long-term stability assessment parameters
Fouad Salimi, Cyrus Ershadi, Vahid Chegini
2023, 42(10): 75-83. doi: 10.1007/s13131-022-2110-5
The wave power in high potential area of the northern Persian Gulf (near to Iranian coastal areas) is assessed by taking into account the temporal and spatial distributions of wave power for a period of forty years. For this purpose, assimilated wind data of European Centre for Medium-Range Weather Forecasting Interim Reanalysis (ERA-Interim), and hydrography data of General Bathymetric Chat of the oceans (GEBCO) are used as SWAN model. Seven locations are investigated in the study area by considering the amount of coefficient of variation, the amount of average annual power, and the short-term and a new long-term (decadal variability index) power stability assessment parameters. The results showed more stability in the eastern parts of the study area and concluded that a narrow line between the point which is in the middle and another point which is in the eastern middle part of the study area may be the best locations for more investigation and the feasibility study for energy converter farms. Also, it is found that the middle part of the study region with about 2.5 kW/m power is the most energetic area. It is concluded that the dominant direction of wave power distribution in all points is the northeast, and this dominant direction has not changed during the forty-year period. It is observed that the mean annual energy increases with a slight slope in the total 40 a, and this increasing trend is more obvious in the fourth decade. Although it is observed that the wave power of the second decade has the most stability and the least variation, the wave power in the fourth decade has the most variation. Moreover, the results showed that the study region’s wave power increase by approximately a mean change rate of 0.027 kW/(m·a); and the maximum change rate of wave power was in the northwest part and the minimum change rate of wave power was in the southeast part which were about 0.036 kW/(m·a) and 0.014 kW/(m·a), respectively.
First assessment of Noise-Equivalent Sigma-Zero in GF3-02 TOPSAR mode with sea surface wind speed retrieval
Junxin Yang, Lihua Zhong, Xinzhe Yuan, Xiaochen Wang, Bing Han, Yuxin Hu
2023, 42(10): 84-96. doi: 10.1007/s13131-023-2215-5
Gaofen-3-02 (GF3-02) is the first C-band synthetic aperture radar (SAR) satellite with terrain observation with progressive scans of SAR (TOPSAR) imaging mode in China, which plays an essential role in marine environment monitoring. Given the weak scattering characteristics of the ocean, the system thermal noise superimposed on SAR images has significant interference, especially in cross-polarization channels. Noise-Equivalent Sigma-Zero (NESZ) is a measure of the sensitivity of the radar to areas of low backscatter. The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level. For TOPSAR, NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range. Therefore, the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data. This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm. A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths. According to assessment with wide-swath TOPSAR cross-polarization data, the GF3-02 TOPSAR mode has a very low thermal noise level, which is better than −33 dB at the edge of each beam, and controlled below −38 dB at the center of the beam. The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users. After discussing the relationship between normalized radar cross section (NRCS) and wind speed, we provide a formula for NRCS related to wind speed and radar incidence angle. Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images, the bias is −0.0048 dB, the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939.
Articles$Marine Chemistry
Prediction of seawater pH by bidirectional gated recurrent neural network with attention under phase space reconstruction: case study of the coastal waters of Beihai, China
Chongxuan Xu, Ying Chen, Xueliang Zhao, Wenyang Song, Xiao Li
2023, 42(10): 97-107. doi: 10.1007/s13131-023-2149-y
Marine life is very sensitive to changes in pH. Even slight changes can cause ecosystems to collapse. Therefore, understanding the future pH of seawater is of great significance for the protection of the marine environment. At present, the monitoring method of seawater pH has been matured. However, how to accurately predict future changes has been lacking effective solutions. Based on this, the model of bidirectional gated recurrent neural network with multi-headed self-attention based on improved complete ensemble empirical mode decomposition with adaptive noise combined with phase space reconstruction (ICPBGA) is proposed to achieve seawater pH prediction. To verify the validity of this model, pH data of two monitoring sites in the coastal sea area of Beihai, China are selected to verify the effect. At the same time, the ICPBGA model is compared with other excellent models for predicting chaotic time series, and root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE), and coefficient of determination (R2) are used as performance evaluation indicators. The R2 of the ICPBGA model at Sites 1 and 2 are above 0.9, and the prediction errors are also the smallest. The results show that the ICPBGA model has a wide range of applicability and the most satisfactory prediction effect. The prediction method in this paper can be further expanded and used to predict other marine environmental indicators.
Articles$Marine Biology
Seasonal implications for taxonomic sufficiency to simplify M-AMBI methodology in the coastal area adjacent to a eutrophic estuary
Chenman Yang, Hongjun Song, Yi Sun, Pengfei Xie, Yuan Liu, Hongjun Li
2023, 42(10): 108-116. doi: 10.1007/s13131-022-2094-1
Taxonomic sufficiency (TS) refers to identifying taxa to a taxonomic level sufficient to detect community changes in stressed environments and may provide a cost-effective approach in routine monitoring programs. However, there is still limited information regarding the seasonal impact of applying TS and its implications for the ecological quality evaluation in the estuarine ecosystem. This study investigated the relationship between the multivariate-AZTI’s Marine Biotic Index (M-AMBI) and environmental variables in three seasons (i.e., spring, summer, and autumn) in the Liaohe River Estuary. We tested the reliability of TS for simplifying the M-AMBI methodology. The results showed that family and genus level data could reproduce the spatial-temporal patterns of community structure at the species level. The M-AMBI values showed a consistent spatial distribution pattern in all sampling seasons, with a decreasing trend with the increasing distance from the estuary mouth. Both genus and family level data performed nearly as well as species level in detecting the seasonal variations of pollutants (i.e., nutrients and total organic content). The family level M-AMBI was feasible to discern stress in the Liaohe River Estuary because of the high aggregation ratios at different taxonomic levels in all sampling seasons. These findings suggest that applying taxonomic sufficiency based on the M-AMBI provides an efficient approach for evaluating ecological quality in the Liaohe River Estuary.
Articles$Marine Technology
Technical development of operational in-situ marine monitoring and research on its key generic technologies in China
Yunzhou Li, Juncheng Wang
2023, 42(10): 117-126. doi: 10.1007/s13131-023-2207-5
In China, operational in-situ marine monitoring is the primary means of directly obtaining hydrological, meteorological, and oceanographic environmental parameters across sea areas, and it is essential for applications such as forecast of marine environment, prevention and mitigation of disaster, exploitation of marine resources, marine environmental protection, and management of transportation safety. In this paper, we summarise the composition, development courses, and present operational status of three systems of operational in-situ marine monitoring, namely coastal marine automated network station, ocean data buoy and voluntary observing ship measuring and reporting system. Additionally, we discuss the technical development in these in-situ systems and achievements in the key generic technologies along with future development trends.
Contributions of annual and semiannual tidal constituents to chart datum in the China seas and adjacent waters
Yikai Feng, Yanguang Fu, Long Yang, Dongxu Zhou
2023, 42(10): 127-136. doi: 10.1007/s13131-023-2231-5
Global uniform chart datum (CD) surface construction is the basic upon which to realize various vertical datums transformation, and is of great importance for geospatial data expression under the same vertical datum. Generally, the CD level is computed by developing the function between tidal constituents’ harmonic constants and time, i.e., the lowest astronomical tide is taken as the lowest predicted tide level by adopting the major constituents over a 19-a period. The CD surface prescribed in China is the theoretical lowest tide (TLT) and is calculated using 13 tidal constituents, i.e., short -period (Q1, O1, P1, K1, N2, M2, S2, K2, M4, MS4 and M6) and long-period (Sa and Ssa) tidal constituents. Although the accuracy in determining short-period tidal constituents has improved gradually, the long-period tide has not been studied thoroughly owing to nonstationary and temporal variations. Previous studies have intended to evaluate the effect of Sa and Ssa tides in the determination of the TLT level for the purpose of determining a more accurate CD surface for the China seas and adjacent waters. Here, the parameters of long-period tidal correction and long-period tidal correction rate were treated as the effect of both Sa and Ssa on the TLT, and the TOPEX/Poseidon and Jason series satellite altimetry data ranged from October 1992 to April 2022 were adopted to analyze the contribution of long-period tidal constituents. Results showed that the average long-period correction value is 10.10 cm (range from 8.57 cm to 14.98 cm), and that the average long-period tidal contribution rate is 14.56% (range from 9.09% to 23.97%) in the China seas and adjacent waters. Finally, data from 82 tide gauge station with at least a 1-a record of hourly observations were compared with satellite-derived result. We concluded that the long-period tidal contribution should not be neglected in TLT construction. Furthermore, to reduce tidal datum uncertainty, accurate extraction of long-period tidal constituents should receive closer attentions.